Having a bit of a trouble-shooting problem. After booleaning some shapes together, I'm trying to fillet some of the edges to a small degree. At the moment, I'm consistently running into roadblocks to find the right edge selection order to get a fillet to work. Is there a way to trouble shoot better to see where the problem is occuring. I'm basically just going by trial and error, selecting various edges to find a combination that works. Just haven't found it yet. I know fillets can be very tricky with complex shapes. I'm including a screenshot of one of the edge areas I try to fillet. Often I get fillets that either just don't have any result or the fillets shoot out of the object in all directions. Any help would be greatly appreciated. I'll send you the moi file by e-mail.

Hi Tree, well one area where fillets can get confused is if you have difficult corner conditions where different fillet pieces are colliding into each other.

So for instance in your case here this is a probably a pretty difficult corner area:

That's sort of an "anti-tangent", you've got 2 edges that touch each other in a sharp corner with exactly opposite tangents. That means the fillet pieces will have some shared surface area in that spot and surface/surface intersections are pretty difficult to calculate in spots where there is shared surface area between pieces rather than a clear distinct line of intersection.

One quick note on fillet selections - you can also select faces to fillet and that will be the same as picking all the edges that belong to that face, so in some cases like this it can be easier from a selection standpoint to grab the face instead.

What fillet radius were you hoping to get there? I tried 0.01 units and it seemed to produce a result.

Some larger radius values such as 0.05 seem to produce a result but with some trimming problems, like for example here is the result at 0.05 units, the fillet surfaces were created but note that it had a problem figuring out that particular corner spot and did not get a fully closed outline there to trim with:

It would probably still be possible to salvage that shape and get the fillet in there by breaking those things into some individual surfaceds, drawing in some lines or something to get a proper trimming outline to use to trim the main parts away, and then trim the fillet pieces with some planes or something and then join the results together. Let me know if you'd like for me to do that, but it is a fairly involved and detailed process so it will take quite a bit of explaining.

Also one reason why you may be getting some weird results with pieces shooting off is there is actually an extra little tiny edge in one spot that you are probably not getting selected, it's here:

If you want to do a lot of filleting like this, you may want to get ViaCAD as a supplement to use along with MoI, ViaCAD uses the ACIS geometry kernel which has had a lot more time spent in the area of fillet development (which is a highly complex process) than MoI's geometry kernel. It seems to be able to handle this corner case better.

Hi Tree, in fact I think the problem is that the fillets themselves do not even actually cross each other at all in that spot, it needs some kind of special logic to build a special connecting piece between the different fillets. The geometry engine that MoI uses just does not handle that particular kind of corner case right now.

Here's a bit more of an illustration - here I have manually constructed the fillets for that spot by breaking your object into individual surfaces and doing the fillet 2 surfaces at a time, which performs a surface/surface fillet which is different kind of calculation than an edge-based fillet:

You can see the fillets don't actually fully run into each other, they kind of touch just at a single point and pass by each other. Also see the attached 3DM file where you can zoom in and rotate around for a better look.

The ACIS modeling kernel knows how to handle this particular situation by trimming the fillets where they barely touch and putting in this connector piece here:

The part that is difficult there is that connector is done with special logic that is dedicated to just this particular corner configuration.

That's what makes fillets so difficult to calculate, many cases such as this one are more complex than just constructing the fillet surfaces themselves, it's handling the logic to connect the pieces together in different ways and handling a lot of different special cases.

It's a lot easier if you are filleting things that have a smooth outline in them rather than sharp or anti-tangent, etc.. type things, because smooth outlines will naturally make the fillet surfaces themselves touch each other and won't need complex corner connection logic.

As always, thanks for the prompt and detailed reply. After a while working with MOI one gets the "feeling" where certain situations will be more difficult to fillet. This was/is one of them. I also noticed the difference where some edges where filleting out and others in and this combination of the 2 trying to come together was causing a problem. Oh I also did notice the little edge hiding in there btw. In most cases, for more complex objects I sometimes have to try a couple times to find the best solution to get a fillet to work. This one was a bit more difficult than usual, so I figured it was time to ask the guru.

Maybe the ACIS modelling kern could be something to consider for future versions of MOI. Although I'm not sure as to the availability of it or the degree to which others using MOI would also need something like it. I just love to fillet since using MOI. :)

Talking about viacad, I really have a bad experience so far, using the 30 days trials :

1) get a lot of trim error when importing MoI .3dm ... so I had so switch to .step, which seems not to be the best format either if I undestand it right.
2) get a lot of random crash, but always using the fillet tool ... complete freezing of the computer (-> reboot)
3) navigation sucks (but that's probably a matter of taste :P)
4) while indeed after all that problems I was able to resolve complex fillet scenario, the command itself is really slow, at a point that I prefer doing simple fillet in MoI, and only the complex one
with viacad.

It's quite hard to evaluate the support when testing , so does you guys have any positive experience with viacad ? aren't here any other ACIS based modeler around that doesn't cost an eye or so ?

So far my experience with ViaCAD is rather positive. It definitely doesn't crash on me. It doesn't run
on Win7 though, at least on my computer. In case I want to edit some Moi models with ViaCad , I export
as "step", "sat" should work ok too.

You might also want to check out Alibre, they have a $99 version, but I'm not sure right now about import/
export capabilities.

SAT is actually the native format of the ACIS kernel, and possibly when importing this format they will avoid trying to mess around with (or "heal" as they call it) the data very much and just suck it in more directly.

> aren't here any other ACIS based modeler around that
> doesn't cost an eye or so ?

It's a pretty new thing to have any ACIS based modelers less than $1000.

> Maybe the ACIS modelling kern could be something to
> consider for future versions of MOI.

Yeah, that is something I'm considering. But unfortunately the ACIS kernel is significantly more expensive and also has a lot more complex royalty based licensing than any other libraries that I currently use with MoI.

Another thing that kind of makes it complex is that it is not quite an entirely 100% "black and white" thing, there are actually some cases that MoI's geometry kernel will fillet that the ACIS one does not handle, although these are in the category of a large fillet radius going around a too-tight bend. I've attached an example, you can fillet this in MoI with a radius of 2 but it won't work in ViaCAD with a radius that large, that's because MoI's geometry kernel can sometimes slice out some areas of the fillet that would otherwise be self-intersecting:

But the ACIS kernel handles way more kinds of corner conditions where fillets need to come together.

SCE will perform that sort of inside corner fillet no problem, but it will not fillet that solid that MG indicated past 2. In fact there are instances where MoI will fillet where SCE will have trouble. The two applications are a pretty powerful pair.

Hello everyone.
I'm not currently an MoI user because it doesn't have some of the features I need, but I have used it and really appreciate the care that's put into its development. I am however, a ViaCAD Pro user and that's the reason I'm replying to this thread. I just wanted to point out that the shape posted by Michael, can be blended in ViaCAD if you use the right option. It worked OK for me with a blend radius of up to 2.4 before giving an error message. To do it successfully you need to use the Variable Blend tool and select the Fixed Width option within that tool. I'm including the SAT file I made, for your scrutiny.